Field of the Invention
The present invention relates to an accumulator which is used in a fluid pressure line such as a hydraulic system or a pneumatic system, and more particularly to a metal bellows type accumulator which employs a metal bellows as a separating means of cushion gas and fluid pressure.
Description of the Conventional Art
The accumulator is a device which is used in the fluid pressure line such as the hydraulic system or the pneumatic system, and is generally used for a pressure control which temporarily stores the fluid pressure by utilizing compressibility of nitrogen gas or absorbs pulsation of pressure generated in the pressure line so as to make the pulsation smooth. There are an accumulator which employs a bladder as the separating means between the cushion gas constructed by the nitrogen gas and the fluid pressure, and an accumulator which employs a piston or a metal bellows as the separating means. Among them, the metal bellows type accumulator can hold down permeation leakage of the gas to approximately 0, and has a high durability.
As the metal bellows type accumulator, there has been conventionally known a structure, for example, as shown in FIG. 5. The metal bellows type accumulator is provided with an outer shell 101, a metal bellows 102 and a vibration damping ring 103. The outer shell 101 is constructed by a cylindrical shell 101a, and first and second end covers 101b and 101c which are provided in such a manner as to close both ends of the shell 101a. The metal bellows 102 is constructed by a bellows main body 102a which is fixed its one end to the second end cover 101c by welding, can expand and contract in an axial direction and is made of a metal, and a bellows cap 102b which is attached by welding in such a manner as to close an opening in a free end side of the bellows main body 102a. The vibration damping ring 103 is attached to an outer periphery of a free end of the metal bellows 102 (the bellows main body 102a). A pressure introducing passage 104 is provided in an opening manner in the first end cover 101b. Further, an outer peripheral surface of the vibration damping ring 103 does not come into close contact with an inner peripheral surface of the shell 101a, and a clearance (not shown) allowing communication of the fluid exists between the both.
An inner chamber of the outer shell 101 is separated into a pressure introducing chamber 105 and a gas chamber 106 by the metal bellows 102. Among them, the pressure introducing chamber 105 is introduced the fluid pressure of the fluid pressure line (not shown) via a pressure introducing passage 104, and the gas chamber 106 in an inner side of the metal bellows 102 is charged the cushion gas such as N2 gas.
This kind of metal bellows type accumulator is structured such that the metal bellows 102 displaces in an expansion and contraction manner so that the fluid pressure introduced into the pressure introducing chamber 105 from the fluid pressure line (not shown) via the pressure introducing passage 104, and the pressure of the cushion gas charged in the gas chamber 106 form an equilibrium state each other. More specifically, when the fluid pressure in the fluid pressure line introduced into the pressure introducing chamber 105 rises, the metal bellows 102 stores the rising pressure by increasing a volumetric capacity of the pressure introducing chamber 105 as well as the bellows cap 102b displaces to the second end cover 101c side together with the compression of the bellows main body 102a and reduces the volumetric capacity of the gas chamber 106. When the fluid pressure in the fluid pressure line comes down, the metal bellows 102 discharges the stored pressure to the fluid pressure line by reducing the volumetric capacity of the pressure introducing chamber 105 as well as the bellows cap 102b displaces to the first end cover 101b side together with the expansion of the bellows main body 102a and increases the volumetric capacity of the gas chamber 106, on the basis of the pressure in the gas chamber 106 which is relatively high. Further, in the operation mentioned above, the vibration damping ring 103 is structured such as to suppress deflection in a radial direction of the free end of the metal bellows 102 (refer, for example, to the following prior art documents).
However, the deflection in the radial direction according to the expanding and contracting operation of the metal bellows 102 is also enlarged in the other portions than the free end of the metal bellows 102, for example, in an intermediate portion in the axial direction of the bellows main body 102a, in some vibration mode, in addition to the free end of the metal bellows 102. As a result, it is desired to prevent the durability from being lowered, even if the metal bellows 102 comes into contact with an inner peripheral surface of the shell 101a by the eccentric operation caused by the vibration.
The present invention is made by taking the above points into consideration, and an object of the present invention is to provide a metal bellows type accumulator which does not cause reduction of durability due to contact of the metal bellows with the inner peripheral surface of the outer shell on the basis of the vibration of the metal bellows in the radial direction.